(a) Technical Field
The present disclosure relates, generally, to a fuel cell separator having an airtight gasket and a method for manufacturing the same. More particularly, it relates to a fuel cell separator having an airtight gasket and a method for manufacturing the same, in which a gasket is suitably integrally injection-molded in a region that requires airtightness of a fuel cell separator to suitably maintain air tightness of each flow field of the separator and to smoothly guide the fluid flow in each flow field.
(b) Background Art
A typical structure of a fuel cell stack is described briefly with respect to FIG. 14 below. Preferably, a membrane electrode assembly (MEA) is suitably located in the middle of the fuel cell stack and preferably includes a polymer electrolyte membrane 10, through which hydrogen ions (protons) are suitably transported, and an electrode/catalyst layer such as an air electrode (cathode) 12 and a fuel electrode (anode) 14, in which an electrochemical reaction between hydrogen and oxygen takes place, suitably disposed on each of both sides of the polymer electrolyte membrane 10.
Preferably, a gas diffusion layer (GDL) 16 and a gasket 18 are sequentially stacked on both sides of the MEA, where the cathode 12 and the anode 14 are located. A separator 20 including flow fields for supplying fuel and discharging water generated by the reaction is suitably located on the outside of the GDL 16, and an end plate 30 for supporting and fixing the above-described components is suitably connected to each of both ends thereof.
Accordingly, at the anode 14 of the fuel cell stack, hydrogen is suitably dissociated into hydrogen ions (protons, H+) and electrons (e−) by an oxidation reaction of hydrogen. The hydrogen ions and electrons are transmitted to the cathode 12 through the electrolyte membrane 10 and the separator 20, respectively. At the cathode 12, water is produced by an electrochemical reaction in which the hydrogen ions and electrons transmitted from the anode 14 and the oxygen in air participate and, at the same time, electrical energy is suitably produced by the flow of electrons.
In the fuel cell stack, the gasket is preferably attached to the separator and serves as a basis for suitably defining each unit cell of the fuel cell stack and suitably functions to maintain airtightness of each of hydrogen, coolant, and air flow fields formed on the surface of the separator. Accordingly, in order to ensure the functions of the gasket, the method of attaching the gasket to the separator and the selection of a material for the gasket during manufacturing of the fuel cell stack are considered.
Accordingly, in the connection structure between the separator and the gasket, the function of preventing hydrogen from being in direct contact with air, the function of preventing coolant from being in contact with hydrogen and air, and the function of preventing fluids (such as air, hydrogen, and coolant) from leaking to the outside are preferably required. Moreover, the gasket suitably arranged between the separators is needed to strongly support the separators.
Accordingly, a metal separator is suitably formed of a metal thin plate having a thickness of 0.1 to 0.2 mm by a molding process such as stamping to have flow fields. This metal separator may therefore considerably reduce the manufacturing time and cost compared to a graphite separator formed by a mechanical process to have the flow fields. However, there are certain considerations in designing an airtight structure.
Therefore, when a pair of plates having flow fields of an oxidation electrode and a reduction electrode are suitably stacked to form a metal separator, and when a gasket is suitably attached to each metal separator, the function of maintaining the airtightness of a cooling surface formed between the pair of plates and the function of maintaining the airtightness of the reactant gases and coolant between a plurality of separators stacked in series are considered. Moreover, the gasket should preferably serve to suitably support the separators and another gasket on the opposite side.
Preferably, the metal separator is required to have an airtight performance suitably higher than that of the graphite separator since the reactant gases and coolant are most likely to leak due to deformation caused by the thin metal plate.
An example of the prior art is shown in FIG. 12, where a connection structure between separators and gaskets is shown. Preferably, a back-up support as an independent structure is suitably introduced to maintain the airtightness of reactant gases and coolant flowing through flow fields of a separator and to serve as a support for another gasket on the opposite side placed on the same line, in which the back-up gasket attached to a gas surface of the separator through which air or hydrogen flows and the gasket attached to a cooling surface through which coolant flows are suitably separately provided.
However, with only the back-up structure, it is difficult to ensure the airtightness of flow fields, through which the reactant gases (such as hydrogen and air) flow, which face each other with a membrane electrode assembly (MEA) interposed therebetween. Moreover, an additional process is required to suitably manufacture the respective back-up gaskets and the gaskets should be suitably separately attached to both sides of each separator.
Another example of the prior art is shown in FIG. 13, in which an additional gasket line (dual seal) is suitably provided to improve the airtightness of reactant gases and the support function. However, in this structure, the gasket structure is complicated and the size of the separator is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.